1. Field of the Invention
The present invention relates to a lens position control device and an optical apparatus having a full-time manual operating function whereby a lens can be moved in the direction of an optical axis through a mechanical cam or the like interlocked with a ring operation member and a focus preset function whereby the lens can be instantly driven and moved to a preset position.
2. Description of Related Art
It is known that some optical apparatuses have a focus preset (hereinafter abbreviated FP) function. For the FP function, an FP storing switch and an FP driving switch are provided on an interchangeable lens. With the FP storing switch operated at a desired focusing lens position beforehand, a focusing lens can be instantly moved to the desired position with a motor by just operating the FP driving switch, even after the focusing lens is driven with the motor by an automatic focusing (AF) action or by a manual focusing (MF) action performed according to the result of focus detection on the basis of an output of an AF sensor or according to the amount of operation on a manual operation ring. This FP function enables the user of the optical apparatus such as a camera, to carry out a photo-taking operation without delay in a case where shooting operation must be instantly be carried out.
Known optical apparatuses of the kind having the FP function include some of automatic focusing single-lens reflex cameras. The automatic focusing single-lens reflex cameras having the FP function must be arranged to electrically operate focusing lenses with motors.
FIG. 12 is a block diagram showing by way of example an interchangeable lens to be used by an automatic focusing single-lens reflex camera of the kind having the FP function. In FIG. 12, full lines indicate electrical connection and broken lines indicate mechanical connection.
Referring to FIG. 12, a lens microcomputer 102 is arranged at a lens body 101 to control various devices within the lens body 101 and to conduct communication with a camera body (not shown) through a contact part 103.
An automatic/manual change-over (A/M) switch 104 is arranged to permit selection of an AF mode and an MF mode. In the AF mode, a result of focus detection made by a focusing detecting device (not shown) is transferred to the lens microcomputer 102 from the camera body. Then, in accordance with the result of focus detection, the lens microcomputer 102 causes a focus driving device 105 which is a drive source to act. The driving force of the focus driving device 105 is transmitted to a focus driving mechanism 106 which is a driving force transmission mechanism. The focus driving mechanism 106 then drives a focusing lens 107 accordingly.
An absolute value encoder 108 and a relative value encoder 109 are arranged to send their detection signals to the lens microcomputer 102. The absolute value encoder 108 is disposed at a part of a transmission mechanism of the focus driving mechanism 106 and is formed, for example, to have a fixed Gray code pattern (not shown) and electric contacts (not shown) opposed to the Gray code pattern. The absolute value encoder 108 is thus arranged to detect the absolute position of the focusing lens 107 by detecting the state of the Gray code pattern through the electric contacts.
The relative value encoder 109 is disposed at a part of the transmission mechanism of the focus driving mechanism 106 and is formed, for example, with a fixed photo-interrupter (not shown) and a pulse plate which is arranged between the light-emitting and light-receiving parts of the photo-interrupter to transmit and block light. The relative value encoder 109 is thus arranged to detect the relative position of the focusing lens 107 by outputting a pulse signal which turns on and off accordingly as the focusing lens 107 moves and by counting the number of pulses of the pulse signal.
The resolution of the absolute value encoder 108 is obtained by dividing the maximum moving stroke of the focusing lens 107, for example, into 32 parts (5 bits). The resolution of the absolute value encoder 108 is thus arranged to limit the movable range of the focusing lens 107. The relative value encoder 109 is arranged to have a resolution which is at least equal to a degree of stopping precision required in bringing the focusing lens 107 to a stop and which satisfies a required rate of focusing accuracy determined according to the F-number and the focal length.
The lens microcomputer 102 controls the focus driving device 105 according to input of information. The lens microcomputer 102 stops the focus driving device 105 when a required amount of moving the focusing lens 107 decided according to the result of focus detection made by the focus detecting device (not shown) and an actual moving amount of the focusing lens 107 detected by the relative value encoder 109 eventually have coincided with each other.
In the MF mode, focus is not adjusted on the basis of the result of the above-stated focus detection. In the MF mode, focus is manually adjusted by operating the manual operation member 110 from outside. The manual operation member 110 is arranged to send, when it is operated, a signal to the lens microcomputer 102 according to the amount and speed of the operation.
Then, in accordance with the signal, the lens microcomputer 102 starts the focus driving device 105 while monitoring the output of the relative value encoder 109, so as to cause the focus driving mechanism 106 to move the focusing lens 107. Therefore, in the MF mode, the user of the camera can move the focusing lens 107 by operating the manual operation member 110 to an extent considered to be apposite to conditions under which the camera is operated.
A zone change-over switch 111 is arranged to permit selection and change-over of the movable range of the focusing lens 107 in the AF or MF mode by operating it from outside. More specifically, the normal movable range of the focusing lens 107 can be selected by turning the zone change-over switch 111 off, while a narrower limited range can be selected by turning the zone change-over switch 111 on. Information on the result of selection of the focusing lens movable range is sent from the zone change-over switch 111 to the lens microcomputer 102. In accordance with the output of the zone change-over switch 111, if the zone change-over switch 111 is turned on in the AF or MF mode, the lens microcomputer 102 controls the focus driving device 105 while monitoring the output of the absolute value encoder 108, in such a way as to inhibit the focusing lens 107 from being driven to the outside of the selected range.
Switches 112 and 113 are provided for the focus preset (FP) function. Both the FP storing switch 112 and the FP driving switch 113 are arranged to be operable from outside and to send their outputs to the lens microcomputer 102. The FP function is carried out as follows.
When the FP storing switch 112 is operated, the lens microcomputer 102 resets a first counter disposed therein to xe2x80x9c0xe2x80x9d. After that, when the focusing lens 107 is to be moved by the AF or MF action, the count value of the first counter is either incremented or decremented by one according to the moving direction of the focusing lens 107, i.e., toward its nearest-distance-end position or toward its infinity-distance-end position according to changes taking place in the output of the relative value encoder 109.
After that, when the FP driving switch 113 is operated, the lens microcomputer 102 causes the focus driving device 105 to drive the focusing lens 107 in the direction of causing the count value of the first counter to become xe2x80x9c0xe2x80x9d. When the count value of the first counter has become xe2x80x9c0xe2x80x9d, the lens microcomputer 102 stops the focus driving device 105. The two FP switches 112 and 113, therefore, enable the user to have the focusing lens 107 promptly moved to a desired position by operating them.
The automatic focusing single-lens reflex camera of the kind having the focus preset (FP) function is arranged as described above.
The lens microcomputer 102 which is disposed within the interchangeable lens of the automatic focusing single-lens reflex camera is arranged to control a diaphragm (not shown) besides the focusing lens. In addition, upon completion of control actions, the action ending signal is sent from the camera body to the lens microcomputer 102, and, then, the lens microcomputer 102 shifts its operation mode to a low power consumption mode for the purpose of power saving. In the low power consumption mode, currents applied to the focus driving device 105, a diaphragm driving device (not shown), etc., are cut off. The lens microcomputer 102 then waits for receiving a lens operating signal from the camera body, detection of operations on the manual operation member and information on the states of switches provided on the interchangeable lens. Upon receipt of the signal or upon detection of the switch operation, the lens microcomputer 102 shifts from the low power consumption mode back to the normal operation mode.
As mentioned in the description of the focus preset (FP) function above, even if the focusing lens 102 is driven by the AF or MF actions after the FP storing switch 112 is operated at a desired focusing lens position, the amount of driving the focusing lens 107 must be continuously monitored after the operation of the FP storing switch 112 in order to have the focusing lens 107 instantly moved to the desired position with the motor by operating the FP driving switch 113.
This process is necessary even in a case where the MF action is performed by a manual operation while the lens microcomputer 102 is in the above-stated low power consumption mode. To meet this requirement, the automatic focusing single-lens reflex camera having the focus preset (FP) function must be arranged to carry out the following sequence of actions.
First step: When the manual operation member 110 is operated by the user, a signal indicative of the amount and speed of the operation is supplied to the lens microcomputer 102.
Second step: Upon receipt of the manual operation signal, the lens microcomputer 102 returns from the low power consumption mode to the normal operation mode.
Third step: Then, the lens microcomputer 102 sends information on the amount and speed of the manual operation to the camera body. After that, an instruction is sent from the camera body to the lens microcomputer 102, instructing the lens microcomputer 102 to drive the focusing lens 107 with information on a focusing lens driving amount.
Fourth step: In accordance with the instruction, the lens microcomputer 102, while monitoring the relative value encoder 109, causes the focus driving device 105 to have the focusing lens 107 moved through the focus driving mechanism 106.
As mentioned above, the camera or optical apparatus must be arranged to only electrically drive the focusing lens with a motor in order to carry out the focus preset function.
However, in a case where an optical apparatus is arranged to have both a full-time manual operating function whereby the lens is to be moved in the direction of an optical axis through a cam member interlocked with a manual operation member and the focus preset function, there arises a problem as follows.
In a case where a manual focusing (MF) operation is performed while the lens microcomputer 102 is in the above-stated low power consumption mode, the focusing lens moves to some extent in association with the manual operation member before the lens microcomputer returns to its normal operation mode. The lens microcomputer 102, therefore, cannot accurately monitor the focusing lens driving amount. If the FP driving switch is operated after that, the focusing lens position obtained by operating the FP driving switch deviates from a desired focusing lens position set by operating the FP storing switch.
It is conceivable that this problem can be solved by arranging the absolute value encoder to have the same resolution as the resolution of the relative value encoder. However, that arrangement is undesirable as it necessitates use of such an encoder that is much more expensive than the absolute value encoder.
It is an object of the invention to provide a position control device arranged to solve the above-stated problem of the prior art, although the position control device uses a relative value encoder and an absolute value encoder which is more coarse in resolution than the relative value encoder without recourse to use of any expensive encoder.
To attain the above object, in accordance with an aspect of the invention, there is provided a position control device arranged to store, as a target position, a position at which a moving member is stopped and to move the moving member to the target position from a position other than the target position, the position control device comprising a first detecting circuit which divides a movable range of the moving member into a plurality of areas and detects in which area of the plurality of areas the moving member is located, a second detecting circuit which detects an amount of movement of the moving member, a storage circuit which stores information specifying a target area in which the target position exists among the plurality of areas and indicating a position where the target position is located within the target area, and a control circuit which controls, in moving the moving member to the target position from a position other than the target position, movement of the moving member on the basis of results of detection made by the first detecting circuit and the second detecting circuit and the information stored in the storage circuit.
In accordance with another aspect of the invention, there is provided a position control device arranged to store a target position for a moving member and to move the moving member to the target position from a position other than the target position, the position control device comprising a first detecting circuit which divides a movable range of the moving member into a plurality of areas and detects in which area of the plurality of areas the moving member is located, a second detecting circuit which detects an amount of movement of the moving member, a storage circuit which stores information specifying a target area in which the target position exists among the plurality of areas and indicating a position where the target position is located within the target area, and a control circuit which controls, in moving the moving member to the target position from a position other than the target position, movement of the moving member on the basis of results of detection made by the first detecting circuit and the second detecting circuit and the information stored in the storage circuit.
The above and other objects and features of the invention will become apparent from the following detailed description of preferred embodiments thereof taken in connection with the accompanying drawings.